Agate Nodule / Weathered Chert

Physical Properties

Hardness: 6.5-7, Color: Brown, tan, yellowish, Luster: Waxy to dull (on weathered exterior), Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Formation & Geological History

Formed through the deposition of silica from groundwater in cavities of igneous or sedimentary rocks. The rough exterior is due to weathering and tumbling in natural environments.

Uses & Applications

Often collected by rockhounds for tumbling or lapidary work. It has little industrial value but is a fun find for collectors.

Geological Facts

Many of these weathered nodules appear unremarkable on the outside but can contain beautiful banding or quartz pockets inside when cut or polished.

Field Identification & Locations

Identify by its hardness (will scratch glass), nodular shape, and waxy luster if broken. Commonly found in riverbeds, glacial till, and desert environments.

Identified on: 4/26/2026

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